A NASA review board has concluded that human error led to the failure of the Mars Global Surveyor (MGS) spacecraft last November.

NASA officials announced at a press conference late Friday afternoon that an overlooked mistake in a June 2006 update to the craft's computer system initiated a chain of events that ultimately caused it to lose battery power. They said that mission staff had followed standard operating procedures, but that the procedures were insufficient to catch the error.

NASA lost contact with MGS on November 2 after routine maintenance. The craft had orbited Mars since September 12, 1997, lasting four times longer than expected. It collected more Mars data than all previous missions combined, including possible signs of liquid water, the selection of landing sites for the Mars rovers and a detailed mapping of the planet's surface and magnetic field.

The review board found that the June update to the craft's computer system sent crucial information to the wrong spot in its memory. The data was supposed to tell the craft where to position its high gain antenna for communications with Earth in case of a problem. The mistake also changed the instructions for controlling the craft's two solar panels.

As a result, a Nov. 2 command instructed one of the solar panels to move farther than it was able. MGS wrongly concluded that the panel was jammed and went into trouble-mode, but it repositioned itself in a way that left one of its two batteries facing the sun, causing it to overheat.

The craft interpreted the heat as a sign that the batteries were charged and therefore stopped charging them. After 10 to 12 hours, it would have lost power and been unable to maintain its position, according to a summary report published Friday on NASA's Web site. "This is an extremely unusual set of occurrences," says board chairperson Dolly Perkins of NASA Goddard Space Flight Center in Greenbelt, Md.

Mission operators were not required to double-check the information they sent or test how it would affect the spacecraft, Perkins says. "Obviously, had these procedures been more rigorous … then perhaps this wouldn't have happened."

Once the mistake had been made, she says, "there wasn't any obvious thing between June and November that would have led somebody to discover it."

NASA project teams are now reviewing the case to decide whether they need to make any changes in the way they operate spacecraft, says Fuk Li, Mars exploration program director at NASA's Jet Propulsion Laboratory in Pasadena, Calif.

"Our other Mars assets are safe," says Doug McCuistion, Mars exploration program director in Washington, D.C., referring to the Mars Reconnaissance Orbiter and Mars Odyssey craft as well as the two Mars Rovers. "We're talking about a spacecraft [MGS] that is essentially a 1980s design." Operators now send higher-level commands that instruct a craft's computer to find its own data, Li says.

NASA convened the internal review board in January to determine what had caused the MGS failure and whether to recommend any procedures to protect other craft.